Nanoparticles for the purpose of drug delivery are defined as smaller than one micron (<1 μm) colloidal particles. This definition includes monolithic nanoparticles (nanospheres) in which the drug is adsorbed, dissolved, or dispersed throughout the matrix, and nanocapsules in which the drug is confined to an aqueous or oily core surrounded by a shell-like wall. Alternatively, the drug can be covalently attached to the surface or into the matrix. Nanoparticles are made from biocompatible and biodegradable materials such as polymers, either natural (e.g., gelatin, albumin) or synthetic (e.g., polylactides, polyalkylcyanoacrylates), or solid lipids. In the body, the drug loaded in nanoparticles is usually released from the matrix by diffusion, swelling, erosion, or degradation (Gelperina et al. (2005) “The Potential Advantages of Nanoparticle Drug Delivery Systems in Chemotherapy of Tuberculosis” American Journal of Respiratory and Critical Care Medicine Vol 172, 1487-1490).
While the unique characteristics (i.e., small size and greater surface-area-to-mass ratio and physicochemical properties) of nanoparticles offer exciting promises in biomedical applications, they also have prompted worries about their potential toxicities. For example in stem cell tracking, superparamagnetic iron oxide (SPIO) nanoparticles have been recognized as a promising tool to intracellular labeling of cells for cellular magnetic resonance imaging (MRI), which plays a key role for developing successful stem cell therapies. Because of the low cellular internalizing efficiency of native SPIO nanoparticles, several modifications of SPIO nanoparticles have been reported to improve the cellular internalization of SPIO nanoparticles. Potential hazards associated with these modifications to stem cells are highly considered. The fact that nanoparticles are manufactured and xenogeneic is a perpetual issue of potential hazard in nanomedical applications.
Erythrocytes have been exploited extensively for their potential applications as carriers of different bioactive substances because of biocompatibility and biodegradability. These carrier erythrocytes may be employed to serve as a reservoir for sustained release or to direct drugs to the reticuloendothelial system (RES), or both.
Red blood cells are about 7.5-8 μm in diameter, which are larger than nanoparticles. Few cells other than macrophages are capable of internalizing particles this large. Generating submicrometer RDV that contain and encapsulate substances can eliminate these problems and fulfill needs for a well-defined nanoparticle drug delivery system.